1. Field of the Invention
This invention relates to a seat buckle and tongue apparatus having a magnetic flux sensor for determining whether a tongue is securely latched within a housing of the seat buckle and tongue apparatus.
2. Description of Related Art
Known seat buckle and tongue assemblies use sensors which are activated when a tongue is inserted into a housing of the seat belt and tongue assembly, in order to detect whether the tongue is securely latched. Conventional seat buckle and tongue assemblies also use magnets and magnetic flux sensors, including Hall sensors, to detect whether the tongue is securely latched.
Sasaki, U.S. Pat. No. 4,943,087 discloses a conventional seat buckle and tongue assembly with a magnetic flux sensor to detect whether a tongue is within a housing of the seat buckle and tongue assembly by detecting a magnetic flux from a magnet mounted on the tongue and thus the presence of the tongue.
Because the magnetic flux sensor taught by the '087 patent detects a presence of the tongue by sensing magnetic flux, any stray magnetic field can cause the magnetic flux sensor to detect a false positive latch condition, such as when the tongue is either not within the housing or the tongue is not securely latched within the housing.
Saito, U.S. Pat. No. 5,218,744 teaches a magnet and a magnet holder molded or encased around the magnet. The magnet and the magnet holder are mounted on a tongue for use with a conventional seat buckle and tongue assembly which has a magnetic flux sensor. The magnetic flux sensor detects a presence of the tongue within a housing of the seat buckle when the magnet on the tongue is positioned near the magnetic flux sensor. The magnetic flux sensor of the 3 744 patent may therefore detect a false positive latch condition.
Yamamoto et al., U.S. Pat. No. 4,920,620 teaches a mechanical sensor for detecting whether a tongue is inserted within a housing of a seat buckle and tongue assembly. The mechanical sensor moves from a disengaged position to an engaged position when the tongue is inserted within the housing and locked with a latch piece.
Positioning a Hall element near a magnet and using a magnetic flux to activate the Hall element is known. When a vane is introduced between the Hall element and the magnet, it is known that the magnetic flux is shunted in a direction parallel to the vane, and the Hall sensor is electronically placed in an OFF state.
Known sensors for seat buckle and tongue assemblies have several shortcomings. For example, in many conventional seat buckle and tongue assemblies a magnet is mounted on a tongue constructed of a ferrous material. The magnetic draw between the magnet and the tongue makes it difficult to handle the magnet during assembly and thus complicates the manufacturing process. Conventional sensing of the latch for seat buckle and tongue assemblies may accidentally activate indicating a latch condition when the tongue is absent thus creating a false positive latch condition. Many conventional sensors attempt to eliminate the false positive latch condition by using a mechanical sensor in lieu of a magnetic sensor. But, mechanical sensors have more moving parts and thus are less reliable than magnetic sensors. The related art is focused on latch sensing and is subject to false positive conditions if the ejector slides back without the tongue being fastened.
There is an apparent need for an inexpensive seat buckle and tongue apparatus having a magnetic flux sensor that can be easily manufactured. There is also an apparent need for a seat buckle and tongue assembly having a magnetic flux sensor which has three sensing states, one of which is used to detect a false positive latch condition. The three sensing states are usefull for a detecting scheme not centered on detection of the latch.